The over-all objective is to determine in a primitive mammal, the North American opossum, and in a primate, the crab-eating macaque monkey, the similarities and differences in the organization of the nucleus of the mesencephalic tract of V (Mes. V) relative to the peripheral structures it innervates and its central nervous system connections. Preliminary data from our laboratories indicate that the Mes. V can be well-labeled for light microscopy in both species using a modification of either the O-Dianisidine (O-Dianisidine (O-D) (de Olmos, '77) or the tetramethylbenzidine (TMB) (Mesulam, '76, '78) methods for demonstrating the presence of horseradish peroxidase. The proposed studies will determine the relationship of the neurons of Mes. V to muscles of mastication (jaw opening and jaw closing muscles), the extraocular muscles, the temporomandibular joint, and the receptors in the teeth and gums. The normal morphology of the neurons and their processes will be analyzed using Nissl and Golgi stains. The efferent connections of the nesencephalic V nucleus will be studied in brains with iontophoretic injections of horseradish peroxidase (HRP) reacted with 3,3', 5,5'-tetramethyl benzidine (TMB) (Mesulam, '78) for light microscopic visualization. The possibility of one Mes. V neuron supplying more than one peripheral structure will be investigated with a double labeling technique using an injection of Evans Blue into one structure and 4'-6-diamidino-2-phenylindol-2-HC1 (DAPI) and primuline into another site. Because these two substances fluoresce at different wave lengths it will be possible to determine if one cell contains only one or both substances. These studies attempt to determine the neuroanatomical substrate for proprioceptive information relative to extraocular muscles, chewing, and the control of the force of the bite. Improper biting force can cause temporomandibular joint destruction and pain as well as increased or deceased bone deposition which may be a primary cause of dentition problems.